The risk factors analysis of the mechanical complications of long-segment orthopedic surgery with pelvic fixation for the treatment of severe kyphosis in the elderly

English Keywords:Severe kyphosis  Mechanical complication  S2AI screw  GAP score

English Abstract:

  【Abstract】 Objectives: To investigate the mechanical complications of long-segment orthopedic surgery with sacral-2 alar iliac(S2AI) screws fixed to the pelvis for the treatment of severe kyphosis in the elderly, and analyze the risk factors. Methods: Patients with severe degenerative thoracolumbar kyphosis who had been placed with S2AI screws for long segment fusion from January 2015 to December 2018 were retrospectively reviewed. A total of 23 patients were recruited, comprising 2 men and 21 women(average age: 68.0±6.5 years, range: 60-84 years). The surgical segment was 9.1±2.4, and the follow-up time was 32.2±6.2 months. The complications of the patients were recorded. Based on the occurrence of postoperative mechanical complications, the patients were divided into group A(no mechanical complications) and group B(with mechanical complications). Visual analogue scale(VAS) for back pain and the lumbar Oswestry disability index(ODI) were compared between the two groups preoperatively and at final follow-up. The pelvic incidence(PI), pelvic tilt(PT), sacral slope(SS), lumbar lordosis(LL), pelvic incidence - lumbar lordosis(PI-LL) mismatch, thoracic kyphosis(TK), thoracolumbar kyphosis(TLK), T1 pelvic angle(TPA), sagittal vertical axis(SVA), Cobb angle(CA), C7 plumb line-center sacral vertical line(C7PL-CSVL), global alignment and proportion(GAP) score were compared between the two groups preoperatively, 1 month postoperatively and at final. Receiver operator characteristic(ROC) curve analysis was used to evaluate the predictive value of sagittal parameters at 1 month postoperatively for mechanical complications, and Logistic regression analysis was performed to determine the risk factors of mechanical complications. Results: At final follow-up, 13 patients had no mechanical complications(group A), 10 patients had mechanical complications(group B), 4 patients underwent revision, and the revision rate was 17.4%. There were no significant differences in gender, age, body mass index, bone density, fixed segment, operation time, method of osteotomy, intraoperative bleeding, and follow-up period between the two groups(P>0.05). There were no significant differences in VAS score and ODI between the two groups preoperatively(P>0.05). At final follow-up, the VAS score was 2.2±0.9 and ODI was (28.6±7.8)% in group A. The VAS score was 3.3±1.2 and ODI was (49.5±9.6)% in group B. Both values of the two groups were significantly improved compared with those preoperatively, and the differences between the two groups were significant(P<0.05). In group A, LL=39.6°±6.7°, SS=28.8°±8.5°, PI-LL=11.4°±11.3°, and the GAP score was 6.9±2.0 at 1 month postoperatively. In group B, LL=24.4°±9.9°, SS=20.2°±8.6°, PI-LL=22.7°±12.5°, and the GAP score was 10.9±2.4 at 1 month postoperatively. The differences were significant between the two groups(P<0.05). At final follow-up, LL=35.2°±8.5°, PI-LL=17.3°±9.6° in group A, and LL=16.3°±9.8°, PI-LL=30.0°±12.1° in group B. The differences were significant between the two groups, and both were significantly different from 1 month postoperatively(P<0.05). The area under the curve for predicting mechanical complications of SS, LL, PL-LL and GAP scores at 1 month postoperatively were 0.762(P=0.035), 0.896(P=0.001), 0.754(P=0.041) and 0.885(P=0.002), respectively, and the best cutoff values were 24.1°, 32.8°, 12.0° and 9.5 respectively. Multivariate logistic regression analysis showed that LL<32.8° at 1 month postoperatively was an independent risk factor for mechanical complications(OR: 48.0, 95%CI: 3.7-622.0, P=0.003). Conclusions: There was still a high incidence of mechanical complications after the long-segment orthopedic surgery fixed to the pelvis for the treatment of severe kyphosis in the elderly. We recommended postoperative SS>24.1°, LL>32.8°, PI-LL<12.0°. Postoperative GAP score≥10 indicated a high risk of mechanical complications.